This invention relates to a lightguide for use in communications or the like, and to a process for producing it. Particularly, this invention provides an optical fiber which, during connection, easily has removed therefrom an unnecessary part (leaked out part) of adhesive and which has excellent optical characteristics, and a process for connecting said optical fiber.
That is, this invention provides a lightguide excellent in optical characteristics from which said unnecessary part of adhesive can easily be removed with organic solvent or the like by curing, at the time of connecting optical fibers, only the adhesive held between the end surfaces of plural fibers without curing the unnecessary part of adhesive protruding out of the end surfaces of optical fibers, and a process for producing it.
For connecting optical fibers, there have hitherto been proposed various processes as follows: (1) a process which comprises tightly contacting together the end surfaces of two optical fibers so that their fiber axes coincide with each other and fusing and bonding the contact part of the end surfaces with hydrogen burner, arc or the like, (2) a process which comprises tightly contacting together the end surfaces of two optical fibers through intermediation of a thermosetting adhesive so that their axes coincide with each other and then heating them to cure the adhesive, and (3) a process which comprises placing silicone oil or the like in a prescribed cylinder, inserting optical fibers thereinto from both ends of the cylinder, uniting both the end surfaces through intermediation of silicone oil and thereby bonding the optical fibers inside the cylinder.
However, in processes (1) and (2), the glass thickens at the bonded part and remains there or the adhesive partially protrudes out of the bonded part and its lump 1 remains there as shown in FIG. 1. As a result, there occurs an irregular reflection at the connected part of optical fiber 2 which has been an important cause of a drop in transmission efficiency when optical fiber 2 is used for optical communication or the like. (In the figure, the arrows indicate the path of transmitted light.)
Process (2) has the problem that the optical axes of the optical fibers slip out of position before the adhesive cures if an adhesive having a long curing time is used and that air bubbles present in the adhesive at the connected part are quite difficult to remove if an instantaneous adhesive of the cyanoacrylate type or the like is used.
Process (3) has the problem that it is low in fidelity in the transmission of optical signals because silicone oil or the like is sealed in the cylinder.